Treatment of cellulose acetate products



UMEED stares FA o at Ft c JOHN FREDERICK BRIGG SfOF SPONDON, NEAR DERBY, ENGLAND, .ASSIGNOR TO AMERICAN CELLULOSE AND CHEMICAL MANUFACTURING COMPANY LIMITED,

A CORPORATION OF DELAWARE.

TREATiunritr or CEILLULOSE ACETATE PRODUCTS.

No Drawing.

To all whom it may concern: 7

Be it lmown that 1, JOHN FREDERICK BRIGGS, a subject of the King of Great Britain and Ireland, of Spondon, near Derby, England, have invented certain new and useful Improvement-s Relating to the Treatment of Cellulose Acetate Products, of which the following is a specification.

This invention relates to the treatment of filaments, threads or fabrics of or containing cellulose acetate, having a lower degree of acetylation than triacetate, with the object of rendering them amenable to dyeing, and to the dyeing of such filaments, threads or fabrics.

The saponification of triacetates of cellulose to remove acetyl groups by treatment with saponifying agents, e. g. heating with alkaline solutions, is generally known,-see for instance Cross and Bevan, Researches on cellulose 11 (1906) page 11;

As is Well known, cellulose triacetates possess but little afiinity for dyes, and especially for direct or substantive colours, which is understandable from a consideration of the fact that the hydroxyl groups of the cellulose are blocked by the acetyl groups; One might therefore expectthat ,lower cellulose acetates would show' an improved aflinity for dyestuffs orfldye better than triacetate.

It wasfound that this is to some extent the case, the lower acetates showing an improvement in regard to the number of dyes which can be applied to them. So far as triacetates are concerned, it has been proposed (see for example British Patent 2067201? 1910) to partially saponify the cellulose acetate in threads, fabrics or. materials made therewith, in order to render them more amenable to dyeing. v

But it has also been found that the lower acetates of cellulose, i. e. which are substantially lower than cellulose triacetate, for

instance those in which from 2 to 3 acetyl groups are combined with one molecule of cellulose (1 11 0 cannot be dyed with dyes in general by the ordinary or commercial methods applicable to non-'acetylated cellulose; for example they cannot be satisfactorily" dyed directly with substantive cotton dyestuffs, and even with basic andacid Specification of Letters Patent.

Patented Ange, 1922.

Application filed April 16, 1921. Serial No. 461,978

dyestufls the possibility of dyeing directly, or with the usual mordants, is restricted to a limited number of dyestuffs.

It is true that the specification of a previous application Serial N 0. 411805 describes a process whereby cellulose acetate threads or fabrics may be rendered amenable or more amenable, to dyeing with basic, acid, substantive, vat or other dyes by treatment with ammonium 'thiocyanate or other thiocyanates prior to or during the dyeing operation, and that this process enables the'lower cellulose acetates, with an acetyl content below that of cellulose triacetate, to be also satis factorily dyed.

The object of the present invention is too provide a new process whereby, While substantially maintaining the weight, mechanical strength, dry or wet, and other technical valuable properties of the original cellulose acetate, threads-or filaments of any degree of acetylation below triacetyl cellulose and especially of cellulose acetate having a content of combined acetyl corresponding to 76 about 2'} acet 1 groups per molecule of celsubjected to a superficial alkaline saponification with a quantity of caustic soda or other alkaline saponifying agent limited to an amount such that the decrease in weight corresponding to the saponification effected thereby is restricted to from about 3 per cent or less to not more thanfabout 10 per cent of the original weight of the cellulose acetate threads or filaments, and preferably to not more than about 5 per. cent of this weight, this saponification being efi'ected at temperatures of between about 60 and about I 80 0., and preferably between about 70 1 00 and 75?. Such a process of saponification, while materially maintaining the weight,

strength and other desirable properties of the cellulose acetate threads or filaments, renders them capable of being dyed with any .dye such as referred to.

the restricted saponification proceeds too slowly and irregularly to permit satisfactory results to be obtained in dyeing. The temably under 0.5%,

perature should therefore not be below C.

and it is usually best to work at about In carrying out the invention the quantity .of alkaline saponifying agent is restricted to about the amount corresponding to theextent of saponification required, that is to say, to a quantity such as Will give this amount of saponification by its approximately complete exhaustion.

This providesa reliable method of con-. trolling the extent of the saponification to the desired degree, so as to maintain substantially the weight and other technically valuable properties of the cellulose acetate threads or filaments as mentioned, and ren-.

der them amenable to dyeing.

My process of treatment of the said cellulose acetate threads or filaments also provides a means of controlling or grading the depth of shade of the dyeing as hereinafter referred to.

As saponifying agent, I use in particular caustic alkali, preferably a solution of caus- 'tic soda, although it is obvious that the principle of my process may be fulfilled by the use of other known alkaline saponifying agents having similar effects. I

It is desirable that the concentration 0 the caustic alkali solution employed should not be higher than about 1% and preferthe best concentration for Working being about 0.1%.

The amount of'superficial 'saponification effected according to the invention corresponds to theemploymentof from about 10% to 3% or less of caustic soda or its equivalent in terms of other alkaline saponifying agents, calculated on the dry weight of the cellulose acetate filaments or goods. The range of 10% to 3% will enable full and level shades to be dyed on the cellulose acetate silks.

When, however, it is desired only to dye the goods to a pale shade, a smaller proportion of caustic soda than that indicated for full shades may be expended in the saponification.

The loss of weight in the form of saponified acetyl groups which the silk undergoes as the result of the treatment of the inventiorivaries directly with the proportion of ,caustic soda or other alkaline saponifying agent expended, and can thus be accurately controlled. For practical purposes this loss of weight may be taken as approximately equal to the quantit of caustic soda used up (mol. weight of aOHzlO; mol. weight OH CO minus H242), that is to say the weight of the acetate filaments, silk or the like, will only decrease to an extent between about 3% or less and about 10% of their original weight, according to the particular pIlyes used, and the depth of shade to be yed.

By regulatingthe amount of the caustic soda or equivalent saponifying agent employed for the process, it is possible to direct or regulate the shade of dyeing according to desire,.which is especially important when it is required to dye light or pale shades.

The dyeing of cellulose acetate filaments or threads or goods containing the same, with employment of my saponification process may be performed in any a propriate way according to two methods w ich I call the pretreatment method and the single bath method. 1

According'to the pretreatment method saponification and dyeing are performed in separate operations, which may be either immediately consecutive, or divided by the interposition of other desired operations, which may be chemical, such as scouring, soaping,

drying, mordanting or the like, or mechanical such as winding, twisting, knitting, weaving, and like textile operations.

According to the single bath method the saponification and dyeing are performed in one bath. I i

In carrying out the saponification as -a separate process I may immerse the goods in a solution containing the predetermined quantity of caustic soda, and heated to the temperature selected for the saponification,

and maintain the temperature of the bath, while working the goods about or otherwise taking steps to ensure uniform circulation or penetration of the liquid, until the caustic soda is neutralized or practically so. The treated goods are removed, rinsed, and. may be scoured if desired. They may then be passed directly and without drying, to the mordanting or dyeing baths, in which they are treated by' known methods similar to those employed for dyeing cotton or cellulose arificial silks. Or else the saponified goods may be dried directly, or after softenin with soap solutions, fatty emulsions, or other suitable finishing agents, and passed through various textile operations before being dyed.'

Goods prepared from cellulose acetate filaments which have undergone pretreatment by my processare susceptible to dyev mg with any dyes, such as substantive dyes,

acid orbasic dyes, vat dyes or sulphur dyes, and by any of the methods for example which are practised in the case of artificial silks such as viscose, cuprammonium, and

denitrated' collodion silks, but they retain special physical qualities, such as superior strength and 1 elasticity in the wet state, which are characteristic of cellulose acetate si k.

'In carrying out the saponification as a separate process or pretreatment I may prepare the saponi-fying bath with hot water to the proportion of 20 to 100 times the weight of cellulose acetate-calculated on the dry weight of the goods, and add to this water a measured quantity of concentrated caustic soda solution, suflicient to'give the pre-de'termined restricted proportion of caustic soda on the dry weight of cellulose acetate in the goods. The quantity of water taken is preferably such that the concentration of caustic soda is not less than 0.1% NaO'I-I. Thus, if I am saponifying. cellulose acetate silk with 10% of its weight of NaOI-I the quantity of water will not be more than 100 times the weightof the cellulose acetate, and if I am saponifying with 5% 'NaOH, I should not take more than times the weight of water on the goods. I may however use other concentrations of soda than those stated, and good results may be obtained by taking water equal to 40 times the weight of cellulose acetate, corresponding to a concentration of 0.25% NaOH, or even 20 times, corresponding to 0.5% NaOI-I. It is evident that the action is more rapid the higher the concentration,

and that if the quantity of water be curtailed, the efficient circulation of the liquor cannot be'ensured. I therefore prefer, fromapractical point of view, to work with a concentration of about 0.1% NaOH. As before stated, however, the concentration should not be higher than 1%.

The saponifying bath containing'the soda is preferably first heated-up to the maximum temperature of saponificationwhich should not exceed about 80 C. I 'generally work at a maximum temperature of 75 (3., but I do not confine myself to this temperature, since it is possible to work less rapidly at 60 C.

If the cellulose acetate goods be contaminated with oily stains, "so that scouring treatment is required, this may either be given before the goods are entered into the saponifying bath, orjwith advantage, soap may be incorporated with the caustic soda in the; saponifying bath in order to effect ously.

Example of pretreatment.-For the pretreatment of 10 lb. of cellulose acetate silk,

I make up a bath with 100 gallons of water at 0., adding concentrated caustic soda lye equivalent to 1 lb. of dry NaOH. The silk is entered into this bath without previous wetting, and is quickly immersed and moved through the liquid or the liquid circulated through the silk, so as to ensure homogeneous distribution of the caustic alkali on the silk. The temperature is maintained at approximately 70-7 5 during the process, care .being taken as far as possible to avoid contact of the silk with the heated surface of the vessel. Under the conditions -Washed and dried and subjected to the usual textile operations and only afterwards dyed,

according to requirements.

In the treatment of union or mixed fabrics composed of cellulose acetate silk and described, the neutralization of the soda and cotton, or other fibre, such as natural silk,

wool, etc., I calculate the caustic soda employed only on the weight of cellulose acetate present in the goods.

With the single bath method any dyes may be used which bear the presence of al-' kali in the bath, which is the case with the entire range of direct or substantive cotton dyestuffs, the sulphur dyestuffs and the vat dyestuffs for example. In this method a known and restricted amount of caustic soda, calculated'on the dry weight of the cellulose acetate in the goods is added to the dyebath, which is preferably heated up to the desired saponification temperature before the-goods vare entered. In this case saponification and dyeing of the cellulose acetate. threads. or goods proceed simultaneously until the predetermined amount of s'apouifying agent has been exhausted, after which dyeingis continued if necessary uhtil the desired shade i's-reached. Such a method is particularly favourable for the even dyeing of pale shades, since the initial resistance of the cellulose acetate is only gradually .overcome by the saponifying action of the eaustic soda, and the dyestufi' is therefore prevented from rushing on to the fibre. The single bath process is, however, equally applicable to the dyeing of full shades, even when the velocity of saponification exceeds that of the absorption of the dyestuif, by continuing the treatment until both the alkali and the dyebath are exhausted.

In carrying out the single bath process, I may, by Way of example, make up a saponifioation bath in the same manner as for the pretreatment process, but adding the desired dyestufi', for instance the requisite quantity of a solution of a substantive cotton dyestufl'. The acetate silk is then entered dry into the combined saponifying and dyeing bath at a suitable temperature, say for in-' stance 70 C. to 75 C., and the dyeing is conducted by working the goods in the usual manner. The dyestufl' solution may be added in portions at various stages of the process in the manner frequently adopted in dyeing artificial silk, and the rate of exhaustion of the dyebath may be controlled by the addition of known suitable adjunct-s, such as soap, in order to promote level dye ing and penetration, or common salt to facilitate the exhaustion of the dyestuff when dyeing full shades, and so forth. If. the dyeing is continued after the caustic soda is substantially exhausted, the temperature of the dyebath may be allowed to fall if desired.

\Vhat I claim and desire to secure by Letters Patent is z- 1. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or.of fabrics of or containing the same, said process consisting in subjecting said goods in an aqueous bath to saponification at a temperature between about and about 80 C. with a quantity of alkaline saponifying agent capable only of efiecting by its exhaustion an amount of saponification corresponding to. not more than about 10 per cent of the original weight of the cellulose acetate threads or filaments, whereby dyeing of the cellulose acetate goods is facilitated while substantially maintaining'their weight and me chanical strength.

2. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containing the same, said process consisting in subjecting said goods inan aqueous bath to saponification at a temperature between about C. and about C. with a quantity of alkaline saponifying agent capable only of effecting by its exhaustion an amount of saponification corresponding to from about 3 to 5 per cent of the original weight of the cellulose acetate threads or filaments. a

3. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containing the same, said process consisting in sub- 4. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containmg the same, said process consisting in subjecting said goods in an aqueous bath tosaponification at a tem erature between about 70 and about 75 with a quantity of alkaline saponifying agent cap-able only of effecting by its exhaustlon an amount of saponificatlon corresponding to not more than about 10 per cent of the original.

Weight of. the. cellulose acetate threads or filaments, the alkaline sa-poni fying agent be-.

ing employed in a concentration of between about 0.1 per cent and about 0.5 per cent.

5. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containing the same, said process consisting in subjecting said goods in an aqueous bath to saponification at a temperature between about 60 and about 80 C. with caustic soda employed in an amount not exceeding about 10 per cent calculated on the dry Weight of the cellulose acetate, substantially as and for the purpose described.

6. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containing the same, said process consisting in subjecting said goods in an aqueous bath to saponifica-tion at ,a temperature between about 60 and about 80 C. With caustic soda employed in an amount of from about 3-to about 5 per cent, calculated on the dry weight of the cellulose acetate, substantially as and for the purpose described.

7. Process for the treatment of threads or filaments of cellulose acetate lower than tri= acetyl cellulose, or of fabrics of or containing the same, said process consisting in subjecting said goods in an aqueous loath to saponifica-tion at a temperature between about 70 C. and about 75 C. with caustic soda employed in an amount of from about- 3 to about 5 per cent calculated on the dry Weight of the cellulose acetate, substantially as and for the purpose described.

8. Process for the treatmentof threads or filaments of cellulose acetate-lower than triacetyl cellulose, or of fabrics of or contain ing the same, said process consisting insubjecting said goods in an aqueous bath to saponification at a temperature between about 60 and about 80 C. with caustic soda employed in an amount of from about 3 to about 5 per cent calculated on the dry weight of the cellulose acetate, the caustic soda being employed in a concentration not higher than about 1 per cent. substantially as and for the purpose described.

9. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containing the same, said process consisting in subjecting said goods in an aqueous bath to saponification at a. temperature between about 70 C. and about 75 C. with caustic soda employed in an amount of fro-m about 3 to 5 per cent calculated on the dry weight of the cellulose acetate, the caustic soda being employed in a concentration of between about 0.1 per cent and 0.5 percent, substantially as and for the purpose described.

10. In a process for the treatment of threads, filaments or fabrics of or containing cellulose acetate lower than triacetyl celso by subjection to partial saponification at temperatures between about 60 and about 80 C. with a quantity of alkaline saponifying agent capable only of efi'ecting a saponification corresponding to not more than about 10 per cent of the weight of the cellulose acetate, regulating the amount of the alkaline saponifying agent for the purofeifecting by its exhaustion an amount of saponification corresponding to not more than about 10 per cent of the original weight of the cellulose acetate threads or filaments, whereby dyeing of the cellulose acetate goods is facilitated while substantially maintaining their weight and mechanical strength.

12. Process for the treatment of threads or filaments of cellulose acetate lower than triacetyl cellulose, or of fabrics of or containing the same, said process consisting in subjecting said goods in an aqueous dye bath tosaponification at. a temperature between about 70 and 7 5 C. with caustic soda employed in an amount of from about 3 to about 5 per cent calculated on the dry weight of the cellulose acetate, substan as and for the purpose described.

In testimony whereof I have hereunto subscribed my name.

JOHN FREDERICK BRIGGS.

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